1. Field of the Invention
The present disclosure relates to an apparatus and a method for performing image processing based on a gray line.
2. Description of the Related Art
When print data for printing a monochrome image on a recording medium is generated, a gray line which connects a white color and a black color is set. Input image data is then converted according to the gray line, so that the print data is generated. In such a case, the white color on the recording medium is determined by a base color (i.e., paper white) of the recording medium such as a printing sheet. Further, the black color on the recording medium is determined by a color of a color material applied to the recording medium, such as ink and toner. An achromatic axis (i.e., the gray line) in a color space is defined as a line connecting a paper white point and a black color point. The black color may be reproduced as a process black in which color materials such as cyan, magenta, and yellow are added to a black color material for the following reason. A tint can be changed by mixing other color materials with the black color material, so that a color such as a deeper gray can be expressed. However, if the paper white point and the black point are displaced from the achromatic axis and the tint is added, the change in the tint becomes conspicuous on the gray line between the paper white point and the black point, depending on how the gray line connects the points. Reproduction of an appropriate gray line may thus be deteriorated.
Japanese Patent Application Laid-Open No. 2008-072208 discusses maintaining reproduction of the gray line in a predetermined lightness range, and, further, controlling the reproduction of the gray line in the other range so that chromaticity smoothly changes from the paper white point and the black point.
However, if hue angles of a gray chromaticity point and a black chromaticity point are greatly different, a feeling of strangeness is provided to a viewer in a portion from a low lightness area to the black color. Such a feeling of strangeness is provided even when the gray line reproduction is controlled so that the chromaticity smoothly changes from the paper white point to the black point.